Recent educational studies have found evidence that measures of fine motor skills are predictive of educational outcomes. However, the precise nature of fine motor skills has received little attention in these studies. With evidence mounting that fine motor skills are an important indicator of school readiness, investigating the nature of this measure and explaining its association with achievement is a key priority for researchers (Cameron et al., 2012). This interdisciplinary study uses theory and measures from neuropsychology to decompose the association between the design copying task and mathematics achievement into fundamental component cognitive processes. The primary aim was to examine the construct validity of design copying as a predictor of mathematics achievement. This study was developed to answer three research questions: (1) Using robust direct measures of cognitive processes, can we replicate the association between design copying and mathematics achievement found in previous studies? (2) How well do the component processes from the visuospatial, sensorimotor, and EF domains together explain this association? (3) Which specific component processes are helpful in explaining the association between design copying and mathematics achievement? To answer the research questions, baseline data from the pilot data of the Minds In Motion Intervention were used. The pilot study took place in several elementary after-school programs located in two demographically different counties in the same Mid-Atlantic state (one in a light farming region and the other in a suburban region). Participants included 145 Kindergarten, first, and second grade students enrolled in school-based after-school programs. The children ranged in age from 5 years 3 months to 8 years 3 months. A multiple mediation model to simultaneously evaluate the contribution of each of the proposed component cognitive processes to the association between design copying and mathematics achievement (Preacher & Hayes, 2008) was adopted. To answer the first research question, the authors determined whether the expected association between design copying and mathematics achievement was observed in the study sample, while controlling for children's age, race, and gender. To answer the second research question, the authors determined the extent to which measures of visuospatial processing, sensorimotor processing, and EF, taken together, mediated this association. To answer the final research question, the authors explored whether specific measures from each of the three domains mediated the relation between design copying and mathematics, while controlling for the other component processes as well as age, race, and gender. Families were recruited into the study in November and December of 2009 and completed a 13- item family questionnaire. This questionnaire included demographic information such as gender, race, and the child's age, which were used as covariates in the analysis. Three findings are evident from this study. First, the results establish a strong direct association between design copying and mathematics achievement (r = .71), a relation suggested by previous research associating fine motor skills with academic achievement. Second, the association between design copying and mathematics achievement is partially mediated by multiple cognitive component processes. Third, because the model only partially explains the association between design copying and mathematics, other underlying cognitive processes that were not examined in this study need to be explored as additional constructs important for explaining this association. The most parsimonious interpretation of results taken as a whole, is that the association between children's performance on the design copying task and their mathematics achievement can be attributed to a common dependence on visuospatial skills, EF, and possibly other cognitive component processes yet to be identified. Such studies are important for moving education science beyond identifying which skills are predictive of school readiness to understanding why these skills are important. A table and a figure are appended.